Anaesthetic administering apparatus with simultaneously variable inlet,outlet and bypass passages



Dec. 16. 1969 R.R.MAC1NTOSH ETAL 3,4

ANAESTHETIC ADMINISTERING APPARATUS WITH SIMULTANEOUSLY VARIABLE INLET OUTLET AND BYPASS PASSAGES Filed Sept' 7. 1965 2 Sheets-Sheet 1 INVENTORS BY fimc vw/ ATTO RNEYS Dec. 16, 1969 R.R.MAC1NTO'SH ETAL 3,

ANAESTHETIC ADMINISTERING APPARATUS WITH SIMULTANEOUSLY VARIABLE INLET, OUTLET AND BYPASS PASSAGES Filed Sept. 7, 1965 2 Sheets-Sheet 2 BY fimm AT TORNEYS United States Patent US. Cl. l28l88 5 Claims ABSTRACT OF THE DISCLOSURE An anaesthetic administering apparatus usable as a plenum vaporizer or as a draw over inhaler having a vapor compartment for anaesthetic agent which has an inlet and an outlet communicating respectively with a carrier gas entry and an exit for carrier gas and anaesthetic vapor. There is a bypass, including an adjustably mounted tube, for carrier gas between the entry and exit and a tapered obturator in the tube. A single adjustment member acting on the tube simultaneously varies the size of inlet port,

of the outlet port and of the fiow passage through the bypass.

This invention concerns improvements in or relating to anaesthetic administering apparatus.

Two main types of anaesthetic administering apparatus are already known namely those known as plenum vaporizers and those of the draw-over type.

Plenum vaporizers are operated under a positive carrier gas pressure generally supplied from cylinders which entrains anaesthetic vapour from a container and delivers it to a patient. Draw-over type inhalers are operated by the breathing of the patient which draws air or oxygen enriched air over a liquid anaesthetic agent entraining the vapour therefrom. Quantitative, temperature-compensated apparatus of both types are unavoidably expensive, relatively large and heavy, and require quite complex means for controlling the concentration of anaesthetic received by the patient.

Circumstances frequently arise which make it desirable to have a small and compact apparatus which is less expensive than the above, known types, and which can also be coupled to the outlet of any main anaesthetic machine or inhaler for the induction and/ or the maintenance of anaesthesia. Moreover, such a small apparatus is particularly useful in dental anaesthesia, because it can be readily held in the hand of the anaesthetist.

It is therefore an object of this invention to provide an anaesthetic administering apparatus of simple construction which complies with the above requirements.

According to the invention there is provided an anaesthetic administering apparatus capable of use as a plenum vaporizer or as a draw-over inhaler comprising an entry for a carrier gas, an exit for the supply of anaesthetic vapour and carrier gas to a patient, a vapour compartment for an anaesthetic agent communicating via an inlet and an outlet port respectively with said entry and exit, a by-pass for carrier gas being provided between the entry and exit, and an adjustably mounted tubular valve slide forming part of the bypass, movement of which serves in operation to vary the size of the inlet port, of the outlet port and of the flow passage through said bypass.

Thus by means of a single valve structure and therefore a single adjustment of the fiow of carrier gas through the bypass and through the vapour compartment to entrain anaesthetic vapour can be proportioned to obtain a desired concentration. We have found that it is possible experimentally to determine the relative shape and dimensions and hence the flow rate/resistance characteristics of the valve structure and the inlet port, outlet port and bypass passage for a variety of anaesthetic agents so as to ensure that for a wide range of intermittent or continuous carrier gas fiow rates, the concentration of the anaesthetic agent in the carrier gas delivered to the patient will not exceed a predetermined value which can be set by adjustment of said valve structure with reference to a calibrated scale.

It will be understood that where reference is made to a carrier gas this can, when the device is used as a drawover inhaler be air, or it can be a medical gas for instance from cylinders or even the output from another anaesthetic appliance.

Such a tubular valve slide preferably includes ports to cooperate with the inlet and outlet ports to the vapour compartment, and a fixed obturator is provided which cooperates with such tubular slide and enables the movement of the valve slide to vary the size of the two parts and the How passage of the bypass.

in one embodiment of the invention the entry and exit of the apparatus each terminate within the apparatus in aligned tubular portions, and a tubular valve slide is longitudinally and telescopically movably mounted with respect to both said portions. To permit variation of the bypass flow passage, the inlet portion may be provided with 21 preferably streamlined strut extending thereacross which serves to carry an obturator of tapered form and which extends into the valve slide. It will be appreciated that the shape of the walls of the bypass and the obturator are determined by the size and shape of the vaporizing compartment, the vaporizing surfaces contained therein, and to some degree by the anaesthetic agent with which the apparatus is desired to be used. The general requirement is that such shapes will together either create or permit a flow of carrier gas to the vapour compartment and through the bypass which will minimise variations in concentration of vapour at the exit.

Generally the inlet port and outlet port to the vapour compartment will be of similar size, the ports in the valve slide which cooperate with them being the same or different size depending on the range of concentrations required and on the anaesthetic agent for which the apparatus is designed.

The inlet port to the vapour compartment is preferably provided with an inlet tube extending downwardly towards the bottom of the chamber to discharge carrier gas therein. Whilst an open ended inlet tube may be used it is preferred to provide a plurality of holes either in the end of the inlet tube or better to provide a number of discharge holes in the walls of the inlet tube adjacent the lower end thereof since this tends to provide a better distribution of carrier gas in the vapour compartment and to limit variations in the output concentration when the flow rate of the carrier gas is varied.

When apparatus according to the invention is used with a continuous, as opposed to an intermittent, fiow of carrier there may still be a tendency for clinically significant variations in the vapour concentration at the exit to occur when the carrier flow rate is altered. We have found that such variations can be kept within tolerable limits by providing a short-circuit path for a proportion of the carrier gas within the vapour component. Thus we may provide a number of small holes in the inlet tube near the upper end thereof, the size, location, and spacing of such holes being determined experimentally for the particular design of vaporizer.

In order to achieve a satisfactory volatilisation of the anaesthetic agent in the vapour compartment it is desirable that the vapour compartment shall have as large a heat capacity as can be provided Within the limits of size and weight imposed on the design and a rapid heat transfer from the environment to the interior of the compartment. In order to increase the heat capacity of the apparatus a temperature-stabilizing tank containing a liquid such as water or anti-freeze solution may be provided in the base of the vapour compartment, such tank being either sealed in manufacture or refillable. Preferably such tank is so disposed in the vapour compartment that it defines with the wall thereof a narrow annular well to receive the liquid anaesthetic agent. Whilst such well can be of constant width over the whole of its depth, the size of the said tank can be reduced or stepped inwardly of the vapour compartment walls so as to increase the size of the well where a larger quantity of anaesthetic agent is required at one time.

With a view to providing a rapid heat transfer to the vapour compartment means are provided for ensuring that the anaesthetic agent to be evaporated is formed into a thin liquid film extending over a substantial part of the inner surfaces of the compartment.

The support for such thin liquid film must have good heat conductivity so as to transfer heat from the environment and must further have an adequate capillary action in order to provide a thin film of liquid extending a substantial distance above the surface of the well of liquid.

We have found that if a wick made of certain types of fine metallic wire cloth is kept in close contact with the inner walls of the compartment both a good heat conductivity and a satisfactory capillary action is obtained. Such wick may either be welded along spaced lines to keep it in heat conducting contact with the walls of the compartment or may be urged into contact therewith for instance by expanding annular springs. It will of course be understood that any metal used for such wick or indeed any other part of the apparatus must be inert to the anaesthetic agents intended to be used. For such a wick in contact with halogenated hydrocarbons and other anaesthetic liquids, we have found that suitable materials are stainless steel, Monel metal or Phosphor bronze. We have found experimentally that wire cloth with a plain weave is unsuitable as a capillary active support in these anaesthetic apparatus, but that more elaborate weaves such as Hollander twill, are suitable and better results are obtained by arranging the cloth so that the strands of the weave extend vertically and horizontally with respect to the surface of the compartment.

A metal cloth support for the liquid will usually be provided over the greater part of the inner surfaces present in the vapour compartment; these include preferably the side and end surfaces of the said temperature stabilizing tank which extends into and forms the bottom of the compartment. If desired further metal cloth can be provided over the upper end of the liquid well in order to prevent splashing of the liquid anaesthetic agent if the apparatus is suddenly or inadvertently shaken.

Instead of specially woven wire cloth, the capillary active surfaces can also be formed from sintered metal. In one form, a sintered metal cylinder can be used as the wall of the vapour compartment; the cylinder is given an integral outer metal skin to form a closed vapour compartment.

The vapour compartment is provided with a level indicator communicating with the Well so that the quantity of liquid in the well can readily be seen, it will be ap parent that a narrow well not only enables small changes in liquid volume to be clearly noted on the level indicator, but ensures that during use of the apparatus the lower end of the capillary active material dips into an adequate depth of liquid, although only a comparatively small volume of liquid is contained in the vapour compartment.

The apparatus is also provided with a filler unit adapted to discharge direct into the well of the vapour compartment, by means of a manually operable filler valve controlling the outlet to the compartment from a funnel into which the liquid may be poured. SinCe there Will often be a pressure of vapour and gas in the compartment after one use and since when refilling air has to be discharged from the compartment it is preferred to provide a release valve in the upper portion of the vapour compartment and to arrange that the control for the filler valve is so :operatively associated with said release valve, that whenever the filler valve is owned, the release valve will first be opened to release any gas and vapour under pressure within the compartment thus avoiding the risk of such gas being discharged through the filler valve, at the same time this arrangement facilitates filling the apparatus with liquid anaesthetic by enabling air to be discharged.

One construction, of apparatus according to the invention will now be described by way of example only with reference to the accompanying drawings in which:

FIGURE 1 shows a section on the line I-I of FIG- URE 2 the setting lever being omitted,

FIGURE 2 shows a sectional view of FIGURE 1 with the inlet shown in full and FIGURE 3 shows diagrammatically and to an enlarged scale a portion of the wick member.

An apparatus according to the invention comprises a body 1 within which is a vapour compartment 2 and a head 3 mounted on the body 1 and carrying the control structure of the apparatus, a cap or cover 4 for the head 3, a level indicator 5 and a filling unit 6.

The body 1 which is of stainless steel is of cylindrical shape and is closed at its lower end by a sealed tank 7 containing an antifreeze solution which serves to increase the heat capacity of the apparatus. This tank 7 is of such a size that a narrow well for a liquid anaesthetic agent is formed between the tank and the wall of body 1.

The level indicator 5 communicates at '8 and 9 with the well so that in use a visible indication of changes in level of the liquid in the well can be provided.

Filler unit 6 which communicates with the bottom or the well at 10 comprises a funnel 11 having a valve controlled partition 12, the portion of the funnel above partition 12 providing a predetermined quantity of liquid. Valve member 13 which serves to control flow of liquid through partition 12, has a cap 14 thereon which is normally held spaced therefrom by a spring 15. A valve actuating member 16 is pivotally mounted on body I and rests in contact with cap 14. This member 16 incorporates a needle valve 17 which normally seats in and closes a vent 18 in the upper portion of the vapour compartment 2.

As will be seen when liquid is to be filled into the well of the vapour compartment an initial downward movement of member 16 will first move needle valve 17 to open vent 1S and release any accumulated gas under pressure in compartment.

2. Only when spring 15 has been compressed to enable cap 14 to seat on valve member 13 will the latter be moved to admit liquid through partition 12 into the well of the compartment 2.

The inside wall of body 1 is provided with a wick member 19 of adequate capillary action to provide and maintain, in operation, a thin film of liquid from the well over a height of several centimetres all rotmd the compartment 2. One example of such a wick is shown in FIGURE 3 and comprises a woven wire cloth of Monel metal wires and wire cloth having 5 warp strands and 14 weft strands. This wick is secured with the weft strands vertical by welding along vertical lines spaced around the wall of the compartment 2 so as to maintain the wick in good heat conducting contact with the body 1 and hence with the exterior and to promote capillary action. This wick 19 extends over the whole depth of the vapour compartment 2.

Metal wire cloth 20 of the same weave as wick 19 is also provided around the sides and end of the tank 7 and across the top of the well. This additional wire cloth 20 not only increases the area of the thin film of vaporizable liquid, but where it extends over the top of the well serves to prevent splashing of the liquid agent if the device is inadevertently shaken.

At the top of the vapour compartment 2 a clamping ring 22 is secured by screws 21 to the head 3 which carries the control structure of the apparatus. A flexible sealing ring 23 is provided between ring 22 and head 3 the arrangement being such that as screws 21 tighten the ring 22 and head 3 together, the sealing ring 23 is urged into gas tight engagement with the wall of vapour compartment 2.

The head 3 has an inlet port 24 and an outlet port 25 which communicate with the vapour compartment 2, a depending skirt 26 being provided within which said ports 24 and 25 are located.

An inlet tube 27 extends from the inlet port 24 downwardly into the vapour compartment. This inlet tube 27 has a number of discharge holes 2 8 spaced around the lower end of the wall of the tube which serve to discharge carrier gas from the inlet port 24 into the vapour compartment 2.

In addition the inlet tube 27 can be provided with a number of short-circuit holes 29, one of which is shown, which serve to provide a fiow path for a portion of the carrier gas between ports 24 and 25, such holes being of assistance in reducing variations in the concentration of vapour at the exit when the apparatus is used under continuous flow conditions of carrier gas.

Head 3 incorporates a tubular member having at one end an entry 30 for a carrier gas and at the other end an exit 31 for delivering a mixture of carrier gas and vapour to a patient. At the entry end of the tubular member, a streamlined cross member 32 extends across a tubular sleeve 33 fixedly mounted in and spaced from entry 30. This cross member 32 carries a tapered obturator 34 on a threaded spindle.

Movably mounted axially of the aligned entry 30 and exit 31 is a tubular valve slide 35.

This valve slide has a convergent-divergent bypass passage 36 therethrough which enables a proportion of carrier gas to bypass the vapour compartment 2 and flow direct from entry 30 to exit 31, anaesthetic vapour from outlet port 25 being mixed therewith. As will be seen bypass 36 co-operates with obturator 34 to vary the flow passage through the bypass upon movement of the valve slide. Furthermore by means of the threaded spindle the axial position of obturator 34 with respect to valve slide can be varied, to enable any desired adjustment to be made to the resistance to flow in the bypass passage 36.

The wall of valve slide 35 is provided with an inlet port 37 and an outlet port 38 which co-operate with the said inlet and outlet ports 24 and 25 respectively and thus upon movement of valve slide 35 serve to control the flow of carrier gas into and out of the vapour compartment 2.

Valve slide 35 carries a toothed rack member 39 the mounting of which extends through a slot 40 in head 3. This rack 39 is engaged by a pinion 41 mounted in the head portion 3 and rotatable by means of a control lever 42, the pointer of which is movable over a scale (not shown) which is disposed on the surface 43 of the cover 4 of the apparatus. This scale will have numbered graduations to enable the user to re-set the control in any given position.

It will be seen that by adjustment of the single lever 42 to a desired graduation mark the valve slide 35 adjusts the size of the inlet port, of the outlet port and of the flow passage through the bypass 36.

Particular sizes of inlet port and outlet port and shapes and sizes of bypass and obturator, as well as the composition and structure of the wick, and the presence and size and disposition of holes 28 or 29 will depend upon the conditions under which the apparatus is to be used, the size and shape of the vapour compartment, and to a less degree on the anaesthetic agent to be used. These structural details can be determined experimentally.

One example however of a vaporizer as described above for use with Halothane, as the anaesthetic agent is given below.

The vapour compartment 2 has a volume of ml. and is lined over its vertical walls with a wick 19 of stainless steel wirecloth of Multiplex weave 36 x 36 mesh.

The wirecloth has 8 warp strands of 41 S.W.G. wire and 13 weft strands of 45 S.W.G. wire.

The tank 7 is covered over its vertical sides and top surface with the same material and the narrow well between tank 7 and body 1 is packed with compressed stainless steel Knitmesh of 45 S.W.G. wire.

The total area of wire cloth provided, excluding the packed wire, is sq. cm.

The entry 30 and exit 31 are circular of 22 mm. diameter.

The valve slide 35 has an external diameter providing a smooth sliding fit in the tubular part of body 3, Which has the same bore as entry 30 and exit 31. The minor diameter of the convergent-divergent passage formed in valve slide 35 is 14 mm., and the included angle of the convergent side is 18.

The obturator 34 has a major diameter of 14 mm. an included angle of taper of 18, and is 16 mm. long. Inlet and outlet ports 24 and 25 are rectangular in plan and are of 0.7 sq. cm. and 0.35 sq. cm. in area respectively.

Two holes 29 constitute a short-circuit for carrier gas and have a combined area of 0.04 sq. cm., and holes 28 which constitute the inlet of carrier gas into the vapour compartment have a combined area of 0.24 sq. cm.

The overall resistance to a continuous flow of 40 litres per min. never exceeds 8 mm. of Water gauge for any position of valve slide 35.

Such a vaporizer is approximately 13 cm. high and of 5.5 cm. in diameter and weighs 1 kilogram.

There has thus been provided an anaesthetic vaporizer of small size, simple construction and low cost. The apparatus can furthermore be easily held in the hand of an anaesthetist. The entry 30 of the device can be connected to another anaesthetic apparatus or to a cylinder for a carrier gas or can be used merely to draw in atmospheric air. The device can thus be used as a plenum vaporizer or as a draw-over inhaler, the flow of carrier gas being either intermittent or continuous as circumstances may require. Whilst precise control of the output concentration to an exact value will not be achieved it is possible to ensure that the output concentration will not exceed a pre-set value as indicated by lever 42 on its scale. The device can readily be used for induction of anaesthesia and under certain conditions if desired for maintenance of anaesthesia.

This vaporizer has furthermore a low flow resistance at the intermittent flow rates which occur in clinical practice, which is a feature of importance in a combined plenum-draw over vaporizer.

In addition it has been found that two units in accordance with the invention can be used in series with th output of one delivering to the input of the other where prolonged anaesthesia is required. Thus one such unit can be used for induction and the other for maintenance of anaesthesia using different anaesthetic agents the two units being controlled according to normal clinical practice. If desired however the two units in series could be used for maintenance of anaesthesia using, say ethyl ether, and together would provide a total concentration for a longer period than could be provided and maintained by a single unit bearing in mind the temperature drop which occurs upon evaporation of liquid. For such latter use manipulation of the valve levers of the two series connected units would need to be in accordance with a predetermined table which can be experimentally determined upon manufacture of the units.

What we claim is:

1. An anaesthetic administering apparatus capable of use as a plenum vaporizer or as a draw-over inhaler comprising: means defining a generally linear flow passage having an entry for carrier gas at one end and an exit for carrier gas and anaesthetic vapor at the other end; means defining a vapor compartment adjacent said passage and having an inlet port and an outlet port communicating with said passage adjacent said entry and exit, respectively; a tubular valve slidable in said passageway and having portions adapted to vary the size of said inlet and outlet ports; and a tapered obturator fixedly mounted in said passage and extending into said tubular valve, the space between said tubular valve and said obturator defining a convergent-divergent flow path whereby movement of said tubular valve simultaneously varies the size of said inlet and outlet ports and said flow passage.

2. Apparatus as defined in claim 1 including an inlet tube extending from said inlet port downwardly into said vapor compartment and having a plurality of discharge holes adjacent its lower end and a plurality of holes adjacent its upper end defining a short-circuit path from said inlet port to said outlet port; and a temperature stabilizing tank having a portion extending upwardly in said vapor compartment and defining therewith a narrow annular well below the lower end of said inlet tube for holding liquid anaesthetic at a level below the lower end of said inlet tube.

3. Apparatus as defined in claim 2 wherein said narrow annular well is packed with compressed stainless steel mesh.

4. Apparatus as defined in claim 1 wherein the inner wall of said vapor compartment is provided with a capillary active layer consisting of a fine metallic wire cloth secured in heat conductive contact with said inner wall.

5. Apparatus as defined in claim 1 including a filler unit adjacent said vapor compartment and having a filler passage communicating with said compartment, a pressure release valve in the upper portion of said compartment, a filler valve controlling said filler passage, and a manually operable valve actuating member arranged to first open said pressure release valve and then open said filler valve whereby to first release any gas pressure in said compartment.

References Cited UNITED STATES PATENTS 257,866 5/1882 Hayes 128l86 733,027 7/1903 Golden 128209 2,872,167 2/1959 Pratt 128-197 XR 2,915,061 12/1959 Edmondson et a1, 128l88 2,941,528 6/1960 Fabian et al. 128-l88 3,072,157 1/1963 Iketani 141Z93 3,077,191 2/1963 Stanton 128l97 FOREIGN PATENTS 682,519 11/1952 Great Britain.

WILLIAM E. KAMM, Primary Examiner 

